1. Field of the Invention
The present invention relates to an active matrix display apparatus and a method for fabricating the same, and more particularly, to an active matrix LED display apparatus having an active matrix consisting of a transistor and a light emitting diode (LED) and to a fabrication method thereof.
2. Description of the Related Art
So far, the display devices are known such as a cathode ray tube (CRT), a plasma display panel (PDP), a field emission display (FED), a thin film transistor-liquid crystal display (TFT-LCD), and an active-matrix organic light-emitting diode (AMOLED).
The advantages and disadvantages of the known display devices are as like as followings.
The CRT is used to create a color image by an electron beam and has the relatively good performance. However, the CRT has problems such as a heavy weight, a wide thickness, and a higher voltage and power consumption. Therefore, the CRT display has been preferably alternated with other thin flat panel display device due to the problem of the thickness.
The PDP is used to display a screen by a plasma discharge in spaces sealed with a front glass, a back glass and partition walls. However, the PDP has problems related to low image resolution and high driving voltage.
The FED uses a field emission cathode to provide electrons that strike colored phosphor to produce a color image. The FED has a high luminance and a high sense of color. However, the FED has problems such as a fast thermal degradation of the cathode and a stability of high vacuum state.
The TFT-LCD is consisted of a bottom plate with TFT element, an upper plate with color filter, and a liquid crystal locating between the bottom and the upper plates. The TFT-LCD controls an emitting light of a back light using a slope of the liquid crystal by a voltage difference. The TFT-LCD is used widely due to the some advantages such as a thin film, a high resolution, and a long life time. However, because the TFT-LCD is one of non-directly emitting elements, it shows bad in the properties of luminance, contrast, sight angle and response speed.
The AMOLED is used to drive an OLED device by TFT element and does not need a back light and a color filter. Therefore, the AMOLED has some advantages such as a simple fabrication, low power consumption, an ultrafine printing and a flexible display. However, the AMOLED has a short life time due to the using an organic electroluminescence diode and is not easy to make a large size due to the difficulty of molding.
The flat panel display (LCD, OLED, FED etc.) is divided to an active matrix and a passive matrix depending on the driving mode.
The passive matrix is consisted of grid of horizontal and vertical electrode lines. The intersection of grid is a pixel for emitting light. The passive matrix is a simple structure, but needs an instantly high luminance to recognize the pixel for short time. Therefore, the passive matrix has some disadvantages such as high power consumption due to the instant luminance, a difficulty in making large size due to the reduction of luminance by the increasing of the line number, and generally a reduction of life time.
On the other hand, the active matrix is consisted of one or more transistors in each pixel and capacitors to store an electric charge for emitting light. Therefore, the active matrix can be turned constantly on a driving state for one frame and be used to produce a display with good efficiency, low power consumption and large size.
The light emitting diode (LED) according to the present invention is a kind of solid element enabling to convert an electric energy into light and is used to an illuminator, a back light unit of LCD and a display apparatus.
Specifically, a non-organic LED is a light emitting element with some advantages such as high efficiency for reducing the power consumption, high color purity for producing the display with good color reproducing ratio, rapid light emitting property due to the using of electron and hole with very high electrical mobility, a long life time, a low environmental pollution due to the using of non-mercury material, and considerably high reliability.
Among display applications, TV is required the most long life time as more than 30,000 hours. The commercial LED is taken more than 50,000 hours of life time and so is sufficient to apply TV display.
Also, the commercial LED has over 100 lm/W of luminous efficiency which is enough to embody a display with an ultrahigh luminance and low power consumption against OLED. Additionally, compared to the TFT-LCD having a back light of LED, the LED can make a display with very thin and considerably low power consumption and without the luminance loss by a liquid crystal, a polarizing film and a color filter.
By the advanced properties of the LED, the AM-LED driving by active matrix can be displayed with some advantages such as a directly emitting light, a long life time against the AMOLED with organic light emitting diode, high luminance and low power consumption. Also, the LED can be displayed with high reliability by good stability in the infinitesimal quantity of water and oxygen which cause serious thermal degradation in the organic light emitting diode.
The personal and household display applications have a medium and small size of display such as a cellular phone, a digital camera, a video camera, a navigation device, a PDA, handheld PCs, a PMP and so on, and also have a medium and large size of display such as a monitor, a notebook, a TV and so on.
Presently, the LED has many advantages compare to the other displays excepting the commercial TFT-LCD and AMOLED. However, for personal and household applications, the conventional LED shows some disadvantages such as an impossibility of a monolithic process for producing one substrate with red, green and blue elements and an expensiveness of a compound semiconductor for molding a whole substrate.
Generally, the commercial LED display has an electric bulletin board apparatus consisted of the LED modules. However, because a display of the electric bulletin board device is formed through matching each LED board and drive board up by the module consisted of one LED element, each pixel of the display can not be miniaturized to apply to the personal and household applications.
The robotic pick-and-place system can be used to assemble hetero devices on a substrate which is not formed by monolithic method. In a micron size of the device, it shows that the efficiency is reducing and the cost of process is increasing.
Consequently, in order to overcome the mentioned problems, some methods, as like as a fluidic self-assembly (FSA) process (e.g., U.S. Pat. No. 5,545,291), are developed to assemble on one substrate with structures, devices, and subsystems needed the incompatible fabricating process using particular forces such as capillary force, gravity, electronic force, and pattern recognition.